Patch "spi: When no dma_chan map buffers with spi_master's parent" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

spi: When no dma_chan map buffers with spi_master's parent

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
spi-when-no-dma_chan-map-buffers-with-spi_master-s-parent.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Kurtz <[email protected]>
Date: Fri, 27 Jan 2017 00:21:53 +0800
Subject: spi: When no dma_chan map buffers with spi_master's parent

From: Daniel Kurtz <[email protected]>

commit 88b0aa544af58ce3be125a1845a227264ec9ab89 upstream.

Back before commit 1dccb598df54 ("arm64: simplify dma_get_ops"), for arm64, devices for which dma_ops were not explicitly set were automatically configured to use swiotlb_dma_ops, since this was hard-coded as the global "dma_ops" in arm64_dma_init().

Now that global "dma_ops" has been removed, all devices much have their dma_ops explicitly set by a call to arch_setup_dma_ops(), otherwise the device is assigned dummy_dma_ops, and thus calls to map_sg for such a device will fail (return 0).

Mediatek SPI uses DMA but does not use a dma channel. Support for this was added by commit c37f45b5f1cd ("spi: support spi without dma channel to use can_dma()"), which uses the master_spi dev to DMA map buffers.

The master_spi device is not a platform device, rather it is created in spi_alloc_device(), and therefore its dma_ops are never set.

Therefore, when the mediatek SPI driver when it does DMA (for large SPI transactions > 32 bytes), SPI will use spi_map_buf()->dma_map_sg() to map the buffer for use in DMA. But dma_map_sg()->dma_map_sg_attrs() returns 0, because ops->map_sg is dummy_dma_ops->__dummy_map_sg, and hence spi_map_buf() returns -ENOMEM (-12).

Fix this by using the real spi_master's parent device which should be a real physical device with DMA properties.

---
 drivers/spi/spi.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

@@ -797,12 +797,12 @@ static int __spi_map_msg(struct spi_mast
 	if (master->dma_tx)
 		tx_dev = master->dma_tx->device->dev;
 	else
-		tx_dev = &master->dev;
+		tx_dev = master->dev.parent;
 
 	if (master->dma_rx)
 		rx_dev = master->dma_rx->device->dev;
 	else
-		rx_dev = &master->dev;
+		rx_dev = master->dev.parent;
 
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		if (!master->can_dma(master, msg->spi, xfer))

@@ -844,12 +844,12 @@ static int __spi_unmap_msg(struct spi_ma
 	if (master->dma_tx)
 		tx_dev = master->dma_tx->device->dev;
 	else
-		tx_dev = &master->dev;
+		tx_dev = master->dev.parent;
 
 	if (master->dma_rx)
 		rx_dev = master->dma_rx->device->dev;
 	else
-		rx_dev = &master->dev;
+		rx_dev = master->dev.parent;
 
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		if (!master->can_dma(master, msg->spi, xfer))

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/spi-when-no-dma_chan-map-buffers-with-spi_master-s-parent.patch